The semiconductor industry has recently experienced technological advances that have permitted dramatic increases in circuit density and complexity, and equally dramatic decreases in power consumption and package sizes. Present semiconductor technology now permits single-chip microprocessors with many millions of transistors, operating at speeds of hundreds of millions of instructions per second to be packaged in relatively small, air-cooled semiconductor device packages. These technological advances have fueled an increased demand for semiconductor devices and products that employ semiconductor devices. A byproduct of this increased demand has been a need to manufacture semiconductor devices having uniform circuit dimensions in an efficient manner as considerations including device speed, reliability and affordability become increasingly important.
One example manufacturing process used in the manufacture of semiconductor devices that affects such considerations includes chemical vapor deposition (CVD). In a typical CVD process, reactant gas is introduced to a chamber containing a semiconductor wafer. The gas is decomposed and reacted at a surface of the wafer to form a thin film of material such as silicon nitride, silicon dioxide or polycrystalline silicon. Many variations in the CVD processing can be used to achieve selected purposes. For more information regarding CVD, reference may be made to 1 S. WOLF & R. N. TAUBER, SILICON PROCESSING FOR THE VLSI ERA—PROCESS TECHNOLOGY 161–197 (1986).
CVD and other film deposition processes have been useful for various types of processes including semiconductor fabrication. However, the demands for improved products continue to present challenges to these and other processes. For example, as semiconductor die circuitry and other structures are scaled to a submicron scale, controlling their dimensions becomes increasingly challenging. One manner in which semiconductor structures are formed includes depositing a film on a semiconductor wafer to be used in controlling the structure dimensions. However, forming films having uniform thickness and/or other properties can be difficult.
In the CVD process, thickness, refractive index, extinction coefficient and other film properties are dependent upon deposition conditions including the concentration, residence time and pressure at which materials are supplied to the deposition process. These conditions are dependent upon the CVD process and the chamber characteristics. In some instances, chamber characteristics make it difficult to obtain a uniform gas supply.
For example, as reaction products are pumped from a CVD chamber during semiconductor wafer manufacturing processes, the pumping action may tend to draw reaction gasses from portions of the chamber in an uneven manner, which in turn affects the deposition conditions. When certain portions of the CVD chamber experience insufficient gas supply, these portions, sometimes including half or more of the chamber, can become unsuitable for CVD. This often means that fewer semiconductor wafers can be processed in the chamber, thereby decreasing output and adding time, materials, labor and overall expense to the wafer manufacturing process. Using existing CVD processes and systems, maintaining a uniform supply of gas over the surface upon which a film is being formed and maintaining uniform process conditions can be difficult or even impossible.